Yet another keg furnace

Discussion in 'Furnaces and their construction' started by Mark's castings, Aug 3, 2018.

  1. Did you balance the impeller?
     
  2. It's off a commercial unit and was balanced.
     
  3. If you forward to 9:19, you can see the blower in operation, there's few things I can do to fix the whine fairly easily by changing the geometry of the blade shape near the impeller periphery. the motor shaft is now drilled up the middle and tapped to take a 6mm bolt and keeper washer to help hold the shaft sleeve in place.



    keeper screw.jpg
     
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  4. _Jason

    _Jason Silver

    Looks good to me.

    I would be curious to put a manometer on that and see how much pressuee it develops.
     
  5. I have a basic water manometer, I suppose I could plumb both blowers into the furnace and see how many inches of water I get. Not sure if running it blocked is a fair test, but it did blow things like clocks off the shed wall first time.
     
    _Jason likes this.
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    Sounds like its good enough! LOL
     
  7. joe yard

    joe yard Silver

    That is a very impressive blower. It would be interesting to take an amp reading during a static run and also during a controlled load. I would think that the first stage of the original blower would have used most of the Hp.
    I am sure that it will work very well. Your workmanship shines and it is built very tight.
    Until you tested it with an amp meter to see how many amps are drawn when under output and input restriction. You could not determine the duty cycle at pressure or vacuum.
    The blower I have will produce quite an input or output pressure and volume but if it is totally restricted. It is over heated quickly. My blower is similar to this one.


    A power steering pump would be a good choice. The average pump displacement is around 1 cu in. If you run one around 500 rpm the 1/2 hp motor you are using would produce over 500psi without overloading.
    If you run this type of pump. The filter should be on the suction side.
    I went
    to the shop the other day and did a bit of work mostly on sorting and organizing with some work on my fuel system.
    The copper tube from the pump runs through the fittings and is unbroken until just below the bottom of the tank, The poly line running up the side is functional but when I find a 6 inch by 1/4 inch pipe nipple. I will put an L on it at and making a nice straight run up the side.
    On the output side I have the fittings for poly hose but I do not have the adapters to N.P.T. pipe yet. I still have to do quite a bit of plumbing. blower.png IMG_2739.JPG
     
  8. Hi Joe, a power steering pump is going to be my next choice if I can't get the engine oil pump running properly. Running kerosene through it may cause lubricity problems so I'll have to start adding waste oil to help a bit. What's your particular blower unit intended for, furnace use?. You would think blocking the outlet air would reduce power consumption and heating.

    In answer to your question about current draw:

    Motor data plate rating is: 8 Amps.
    Full load (no obstruction): 8.4-8.7 Amps (5-10% overload)
    No load (The air outlet blocked): 3.7-3.9 Amps
    Motor off: 0.25 Amps draw so there's some interference/inaccuracy.

    I expect to run the motor below half airflow rate so the current draw will be well within rated consumption, say 6 Amps. I got very lucky with the blower power consumption this time. The blower now has a steel tube stand with carrying handle on top, it's very heavy as the motor body is cast iron, going to be fun to lug it around after a days casting.

    blower stand.jpg

    Outlet blocked (no load)
    blower current stalled.jpg

    Outlet wide open (full load)
    blower current full load.jpg
     
    Last edited: Feb 4, 2019
  9. I ran both of my 1/2Hp 240V motors used to drive my pump/filter unit today. Both of these measured about 2/3rd rated current with no load and ran fine despite popping their overloads when driving the fuel pump. Next I had a close look at the pump and after a bit of head scratching realized the high pressure viton shaft seal I'd fitted had popped: using the grease gun to lubricate the shaft caused some kerosene squirt past the seal. So it seems at 55 PSI or so, the kerosene fuel pressure is high enough to pop the seal just enough to leak and then wash the grease off the shaft and allow it to seize. I now have a machined steel cap to go over the seal and hold it firmly in place, I'll give it a test run tomorrow monitor the load current and see if it fixes the problem. Next option would be to bore the iron casting and fit a bronze bush for the shaft and maybe a drive coupling instead of the side loading belt and pulleys.

    Fingers crossed...
     
  10. Furnace extension: it's not the girth that counts, it's the length...or so I keep telling myself. My furnace is a fairly faithful copy of an existing propane furnace that works very well. On diesel, kero and waste oil it runs well enough to melt bronze and brass but iron just gets soft and sweats beads of iron without really liquefying. Based on earlier, taller, test bed furnaces and this furnace too, I notice the bottom of the furnace runs rich with soot deposits while the exhaust is still burning as it exits the lid. So over the last month or so, I've added 50% extra length to the furnace, the theory being that the hot gasses will be in the furnace now for 50% longer and hopefully burn completely. Due to crucible size considerations there wasn't much of a combustion chamber under the crucible with the original sized furnace, so now there's scope for space under the crucible for a combustion chamber area. I'll start with a 6" x 5" diameter plinth to raise the crucible up which should give a significant volume below the crucible which it did not have before. I can now fit a AT30 crucible which is the same diameter as an AX20 but taller, I can't buy 20 sized silicon carbide crucibles locally without a special order where the 30 size are common.

    The complete unit is only 4" taller than before as I've cut the four legs off the bottom to lower it a bit, so the height is not too bad, I can work with it like that.


    Now with added length!
    furnace extension 2.jpg


    Bleach bottle sized plinth
    plinth 1.jpg

    I may drill the plinth for a steel peg to locate it
    plinth 2.jpg

    Plenty of height available to get the crucible position right
    furnace bore 2.jpg


    Roughly 20 size clay graphite crucible in place
    furnace bore 1.jpg
     
    Last edited: Jun 8, 2019
    joe yard likes this.
  11. You sure do nice work!
     
  12. I am a weld grinding guru!
     
    Jason and oldironfarmer like this.
  13. Edit 31/8/19: I made a mistake: fuel consumption was 30 litres per hour not 60 litres stated below.


    So I had the chance to run the modified furnace with the extra height and trialing a new nozzle assembly. On the first run it ran satisfactorily and at the upper end of the fuel flow and airflow I had this unstable oscillation where it would run normally and then the flame would retreat under the crucible and the furnace would roar/buzz like a ramjet engine exhaust. I took a punt and fitted a flame can behind the nozzle and ran the furnace again: normal fuel/air setting it runs normally with yellow flame and heat up high in the chamber about level with the rim of the crucible (glowing orange). On the highest air and fuel flow settings, the thing roars like a ramjet and a blue flame now does a lap of the plinth before turning orange and exiting. It burns clean and loud and fuel flow would be 12-15 US gallons per hour (60 litres) at 65 PSI fuel pressure. I'm thinking if I could remove the plinth and get the crucible in the blue flames it should work well. It does seem to be a different mode of combustion I haven't seen before, it would be nice to get it to occur at lower fuel flow rates though. Anyone seen this mode of combustion before?.

    First part of the video is "Ramjet mode" and shows the dull red crucible glow after 5 minutes run time from cold, second half is the furnace running at normal, lower throttle settings:

     
    Last edited: Aug 31, 2019
  14. Melterskelter

    Melterskelter Gold Banner Member

    Mark, Wow, 12-15 gallons per hour! That is a huge fuel burn rate.

    What is interesting about the ramjet first half video is that the furnace looks so cold inside. Could it be that with the very large airflow that the fuel/air mix is blowing through the furnace at such a high rate that only the very initial part of combustion is happening within the furnace and the rest is comleted outside? If so, then just the "cool" part of the flame is in the furnace and the heat is actually generated in large measure outside the furnace?

    I would expect that after a burn after a burn with 12 gallons per hour of good heat extraction you would be picking your furnace up with a ladle!

    Denis
     
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  15. Melterskelter

    Melterskelter Gold Banner Member

    Attached Files:

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  16. Jason

    Jason Gold

    That thing did sound like a ram jet. I can tell you start temps on a jet engine are wayyyy hotter during the start than at maximum thrust. Why is this? There isn't as much air moving through the engine due to lower air flow. I bet that crucible was hotter back down at normal speed and lower fuel flow rate.
    But I'm just a pilot. Which stands for,
    P
    oor
    I
    ntelligence
    L
    ots
    Of
    T
    raining.
     
    Mark's castings likes this.
  17. Denis: that article about flame combustion is a bit of an eye opener, I'd always assumed blue flames are hottest and tuned out any bright white flames, more experiments are needed. Edit: In answer to your question, there doesn't seem to be much heat above the crucible and exhausting the furnace, it seems to be underneath the crucible where there's about a 5" by 4" diameter plinth and plenty of room.

    It does run much hotter at the lower combustion rates. In ram jet mode the crucible is running quite cool too, it's full of half melted iron stuck in there from earlier experiments so it looks darker. The combustion seems incredibly clean too, no hint of smoke at all. After that 9-10 minute run the 20 litre / 5 US gallon drum was half empty so 15 gallons per hour is about right. I'd tested one nozzle with water to estimate flow rate and it seems to flow higher with fuel.

    It's all a bit new to me and I'm still trying to get my head around what's happening. There is also the field of thermoacoustics coming into play to some extent: the conversion of heat into sound energy. Pulsating sound waves can create a very well defined hot area and cold area in pulse jet motors. If I can tune out the sound, keep the same high clean burn AND couple the heat to the crucible, I'd be on a winner. I'll raise and lower the plinth height next and see if I can get the crucible into a hot region.

    One interesting point is the first run without a flame can (not shown in the video) the combustion was unstable and kept alternating between the two modes but ran quieter: the ramjet noise came in louder with the flamecan.
     
    Last edited: Jul 30, 2019
  18. Melterskelter

    Melterskelter Gold Banner Member

    So here is what I am having trouble wraping my head around. Yesterday I melted 30 pounds of iron at a fuel flow rate of 2.2 gallons per hour in 45 minutes. My furnace was white hot all over inside as was the crucible and plinth. You were burning fuel at a rate 7 times that and burned 3.5 times the amount of fuel in 1/2 hour that I burned in 1 hour. If you extracted the energy inside the furnace that was contained in the fuel you burned, why wasn't the empty furnace white hot (or melted into a puddle for that matter) throughout? Where did all that heat energy go?

    Denis
     
  19. PatJ

    PatJ Silver

    Translated, that means "you are dumping too much fuel into your furnace, and there is no chance of it combusting in that small of a space.".

    .
     
    Jason likes this.
  20. Hi Denis, there is a real life example of a similar high rate of burn without melting the combustion area: a jet engine, more specifically a ramjet engine. This furnace is loud in a way that it's maxed out the audio waveform of the camera when looking at it in the video editing software. I'm also having trouble wrapping my head around what's happening too. I did discuss it with Peter, my foundry expert, he had a larger furnace that could be run in the same way: when running flat out it generated a loud roar heard blocks away and not much heating. This was at night in the industrial area of town and the local bakery staff blocks away told him they could tell his furnace was running wrong that night. Peter had his foundry expert Laurie take a look (a qualified engineer who worked on an Australian WW2 turbojet engine project). Laurie just laughed, told him there was an upper limit for transferring heat to the crucible, that his burn rate was too fast for this to happen and told him to run the furnace at lower throttle settings. They ran the furnace at a more normal setting and it ran fine: two shifts a day making aluminium and bronze castings. They just couldn't speed up the melting times with more fuel.

    Edit: My current working hypothesis is with the high speed gas flow, I'm losing conductive heat transfer and only keeping the thermal radiation. I know that when using extruded finned heatsinks for cooling electronics you can boost cooling by using pancake fans for airflow but you can make things worse with too much airflow: the airflow is too fast to couple heat from the fin to the air. The furnace is the reverse of heatsink example, you are trying to extract heat from the hot gas but the flow is too fast to transfer heat to the crucible through conduction.

    To me the video does show complete combustion, there's no hint of a smell of it burning rich and certainly no smoke in the video, some sort of woven platinum mesh in the exhaust stream would be the ideal test to see if there's unburnt fuel.
     
    Last edited: Jul 31, 2019

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